**CCTP Seminars: Fall 2013**

**A Dimensionally Deconstructed Holographic Superconductor**

Speaker: | Dylan Albrecht |

Department: | University of Crete |

Slides: | [PDF] |

Time: | Tuesday 27 August 2013 at 10:00 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | I will discuss my work on using the technique of dimensional deconstruction to build a lower-dimensional model of one of the first holographic s-wave superconductors. The model consists of multiple scalar fields which condense at a critical temperature, and exciton fields with interactions governed by hidden local symmetries. Imposing specific, discretized expressions of the continuum boundary conditions this model has some similar phenomenology to the higher-dimensional holographic superconductor. |

**Breaking translations in holography**

Speaker: | Aristomenis Donos |

Department: | University of Cambridge |

Time: | Monday 9 September 2013 at 11:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | Gravitational backgrounds which break translational symmetry either spontaneously or explicitly have been recently considered in the context of AdS/CMT. After giving a brief overview/motivation for both kinds of constructions I will discuss the basic steps for solving the corresponding systems of partial differential equations. |

**Holographic Superconductors at the phase the transition**

Speaker: | Francesco Aprile |

Department: | University of Crete |

Time: | Tuesday 10 September 2013 at 10:30 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | Holographic superconductors may arise as the low temperature phase of black branes. In case in which the phse transition to the superconducting phase is at least second order, several critical exponents can be calculated. In the more general setup of bottom-up model, I will review how these critical exponents can be obtained from a matched expansion and how Rushbrooke Identities of a scaling theory are recovered from holography. |

**The holographic pathway**

Speaker: | Daniel Fernandez |

Department: | University of Crete |

Slides: | [PDF] |

Time: | Tuesday 10 September 2013 at 11:00 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | In this short presentation, I will overview my PhD results and present a few ideas of intriguing aspects of the gauge/gravity duality that could be moved forward in order to extend the usefulness and/or our understanding of this topic. |

**Toward researching holography in Crete**

Speaker: | Takaaki Ishii |

Department: | University of Crete |

Time: | Tuesday 10 September 2013 at 11:30 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | In the first part of this talk, I discuss effects of thermalization on the meson sector of the N=2 SQCD using the gravity dual. We consider dynamical embedding of the probe D7-brane in a fast thermalizing background of D3-branes. We find that new meson melting which was not seen in static embedding occurs due to the thermalization. In the second part, we discuss an s-wave holographic superconductor coupled to a massive vector field. In this model, effects of the massive vector field appear in the superconducting phase. We show that as a result the behavior of the optical conductivity in low frequencies is affected such that the real part is enhanced. |

**Transport Phenomena and anomallies**

Speaker: | Francisco Pena-Benitez |

Department: | University of Crete |

Slides: | [PDF] |

Time: | Tuesday 10 September 2013 at 13:00 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | The last years reappeared an increasing interest on quantum anomalies due to the discovery of a new set of conductivities which are directly related with the presence of triangle anomalies. These conductivities could lead to the observation in the lab. of the so called Chiral Magnetic, Separation and Vortical effects. The understanding of these effects is of interest to explain (maybe) the data coming from Heavy Ion Colliders as RHIC and LHC and also just for theoretical reasons. This program has produced a better understanding of relativistic hydrodynamics, and the effect of the quantum anomalies of the underline QFT, can imply on it. In this seminar I will try to review the progress on the topic in the context of pure hydrodynamics, thermal field theory at weak coupling and strongly coupled theories in the context of holography. |

**Some condensed matter systems from multi-charge black holes**

Speaker: | Jie Ren |

Department: | University of Crete |

Time: | Tuesday 10 September 2013 at 13:30 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | I will talk about the condensed matter applications of maximal gauged supergravities in AdS_4 and AdS_5. These systems have distinctive features due to their different IR geometries. |

**Holographic Type II Goldstone bosons and Landau criterion**

Speaker: | Karl Landsteiner |

Department: | Autonomous University of Madrid |

Slides: | [PDF] |

Time: | Monday 7 October 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | The Goldstone theorem asserts that a broken, global, continuous symmetry results in at least one massless mode. It does however say nothing about the number of such modes nor does it demand the Goldstone mode to have linear dispersion $E~ c k$. In recent years non-standard Goldstone modes whose number does not correspond to the number of broken symmetries and whose dispersion relation is not linear have attracted renewed interest. In my talk I will first give a brief review of the recent new results on such "type-II" Goldstone modes and then discuss two holographic models featuring type II Goldstone modes in their quasinormal frequency spectrum. On the way I will also discuss how the Landau criterion for superfluidity is realized in holography and demonstrate that theories with type II Goldstone bosons are superconductors but not superfluids. |

**Chiral Anomalies and Transport Theory**

Speaker: | Karl Landsteiner |

Department: | Autonomous University of Madrid |

Slides: | [PDF] |

Time: | Tuesday 8 October 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | One of the most fundamental property of relativistic quantum field theories is the presence of chiral anomalies. In a theory of chiral fermions not all classical symmetries can be preserved at the quantum level. In the recent years it has become clear that chiral anomalies play also a distinguished role in the transport theory and the hydrodynamics of relativistic fluids. They give rise to new, dissipation-less transport phenomena such as the Chiral Magnetic Effect (CME) and the Chiral Vortical Effect (CVE). I will discuss the theory of the CME and the CVE at weak and strong coupling and their realization in the Quark Gluon Plasma or in advanced (and still hypothetical) new materials, the so-called Weyl (semi-)metals. |

**The Trailing String in Confining Holographic Theories**

Speaker: | Francesco Nitti |

Department: | APC, Paris |

Slides: | [PDF] |

Time: | Tuesday 22 October 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | The gravity dual of a single heavy probe quark in AdS/CFT is a fundamental string trailing behind the quark in the bulk geometry, with the quark as its UV endpoint. In the deconfined, black hole phase, this configuration allows to compute holographically the energy loss and diffusion parameters for the quark trajectory. In this talk I will discuss the trailing string dynamics in a confining geometry, which displays features such as as the existence of long wavelength modes with viscous dynamics in a confining phase. |

**Ads/CFT, holography and condensed matter physics**

Speaker: | Elias Kiritsis |

Department: | University of Crete |

Time: | Tuesday 29 October 2013 at 11:15 |

Venue: | Physics Department Seminar Room |

Abstract: | This seminar will provide a hopefully pedestrian introduction to the AdS/CFT correspondence and its off-springs that come under various names, (like holographic techniques). The key idea is that quantum (field theory) systems in some strongly-coupled limits can be described by semi-classical gravitational theories in higher dimensions. The goal is to use such ideas to address strongly coupled problems in condensed matter physics. A simple exposition of basic ingredients of holography will be given, with insights of what questions are easier to address and which not. A list of interesting problems will be also given where holographic techniques can be applied. The seminar is tuned to a non-expert audience. |

** Universal hydrodynamics for Quantum Critical Points with Lifshitz scaling**

Speaker: | Bom Soo Kim | |

Department: | Tel-Aviv University | |

Slides: | [PDF] | |

Time: | Tuesday 29 October 2013 at 14:15 | |

Venue: | The 2nd floor seminar room of the physics department | |

Abstract: | We formulate universal hydrodynamics for the theories with Lifshitz scaling, both in relativistic (Lorentz) and non-relativistic (Galilean) contexts. One surprising new result is the discovery of two new universal transport coefficients, one dissipative and one dissipationless, allowed by the absence of boost invariance. It is compatible with the Landau frame condition and positivity of local entropy current. We explain the effects of the new term in detail and provide verifiable experimental consequences. Our results are also applicable for the Lorentz or Galilean invariant systems with broken boost invariance. This has never done before in the literature as far as we are aware. |

**Unquenched massive flavors and flows in Chern-Simons matter theories**

Speaker: | Niko Jokela |

Department: | Universidade de Santiago de Compostela |

Slides: | [PDF] |

Time: | Thursday 7 November 2013 at 15:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | I will describe the construction of the holographic dual to the 3d ABJM with unquenched massive flavors. The background consists of a running solution representing the RG flow between two fixed points, at the IR and at the UV. The flow is generated by changing the quark mass m_q. When m_q is very large we recover the original unflavored ABJM solution, while for m_q very small our solution becomes asymptotically equivalent to the one found recently for massless smeared flavors. I'll discuss the effects of the dynamical quarks as their mass is varied on different observables, such as the holographic entanglement entropy, the quark-antiquark potential, the two-point functions of high dimension bulk operators, and the mass spectrum of mesons. |

**Toward the real time dynamics of periodically driven holographic superconductor**

Speaker: | Hongbao Zhang |

Department: | Vrije Universiteit Brussel and The International Solvay Institutes |

Slides: | [PDF] |

Time: | Thursday 14 November 2013 at 15:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | In this talk, I shall report our recent work, which is supposed to be a first step towards holographic investigation of the real time dynamics of periodically driven systems at strong coupling. After a quick motivation for AdS/CFT in the dynamical setting, I will show our numerical result for the real time dynamics of holographic superconductor driven by an alternating electric field. In particular, I will demonstrate the late time dynamical phase diagram for the large driving frequency, which is separated into three distinctive behaviors, namely under damped to the superconducting phase, over damped to the superconducting and normal phase, can be well understood by the low lying spectrum of quasi-normal modes in the time averaged approximation. If time permits, I would also like to give a glimpse of our upcoming work on a new holographic phase, namely the holographic superconductors nested in charged density waves. |

**Universal scaling properties of holographic low-temperature phases**

Speaker: | Blaise Goutéraux |

Department: | NORDITA, Stockholm |

Slides: | [PDF] |

Time: | Tuesday 19 November 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | In this talk, I will explain how holographic low-temperature phases can be classified, either when translation invariance is preserved or broken homogeneous, by introducing appropriate scaling exponents. I will show how these control physical properties of the dual field theory such as thermodynamics and transport coefficients. In particular, I will comment on the role of the conduction exponent in distinguishing between insulators and bad metals. |

**Holographic massive gravity**

Speaker: | David Vegh |

Department: | CERN |

Time: | Tuesday 26 November 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | We study finite density holographic theories on a background lattice. The presence of the lattice induces an effective mass for the bulk graviton via a gravitational version of the Higgs mechanism. Momentum is not conserved and the conductivity in the boundary theory exhibits a Drude peak. |

**AGT and the genus expansion**

Speaker: | Amir-Kian Kashani-Poor |

Department: | LPTENS, Paris |

Time: | Thursday 28 November 2013 at 15:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract | The AGT correspondence relates conformal blocks in 2 dimensional conformal field theory to instanton partition functions of gauge theory. Motivated by their relation to string theory, the latter can be represented in terms of a generalized genus expansion. In this form, modular properties previously hidden become manifest. We will study the interpretation of the genus expansion from the point of view of conformal field theory, and present a method for computing the modular coefficients of this expansion via CFT techniques. |

**Real-time dynamics of the quark-gluon plasma from the lattice**

Speaker: | Marco Panero |

Department: | IFT Madrid |

Slides: | [PDF] |

Time: | Tuesday 3 December 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | Jet quenching is an important experimental signature for the formation of strongly coupled quark-gluon plasma (QGP) in heavy-ion collisions. The main theoretical tools that have been used to describe this effect, which is related to the energy loss and momentum broadening of hard partons moving through the deconfined medium, include weak-coupling expansions and holographic computations. On the other hand, the dynamical, real-time nature of this phenomenon has prevented a direct approach via QCD simulations on a Euclidean lattice. In this talk, however, following an idea originally proposed by Caron-Huot, it will be shown how one can extract non-perturbative information on jet quenching from the analysis of suitable gauge-invariant operators in a dimensionally reduced effective theory (electrostatic QCD), that can be directly studied by Euclidean lattice simulations. After an overview of the physical problem under consideration, and an introduction to the basics of lattice QCD, the results of a recent, high-precision lattice study of jet quenching (reported in arXiv:1307.5850) will be presented. |

**Bound states - from QED to QCD**

Speaker: | Paul Hoyer |

Department: | University of Helsinki |

Time: | Tuesday 10 December 2013 at 14:15 |

Venue: | The 2nd floor seminar room of the physics department |

Abstract: | The principles and properties of QED bound states are useful for understanding hadrons in QCD. Equal-time atomic wave functions transform dynamically under boosts. Dirac states in D=1+1 have a continuous spectrum and unnormalizable wave functions, reflecting a sea of electron-positron pairs. Born-level positronium states in D=1+1 have non-trivial Poincaré invariance, a discrete spectrum and parton distributions with a sea-like enhancement at low x_{Bj}. These methods may be extended to QCD in D=3+1 dimensions. |

**Coulomb's Law in anisotropic media**

Speaker: | Martin Luling |

Department: | Schlumberger, Paris |

Time: | Friday 13 December 2013 10:30 |

Venue: | The 1st floor seminar room of the physics department |

Abstract: | Coulomb’s law in vacuum or in isotropic, dielectric media has been well known since the early 19th century. The electrostatic potential for a point charge falls off like 1/r, producing a radially polarized electric field and displacement current. In anisotropic media the electrostatic potential also has a close-form solution. For this solution, the concept of a pythagorean distance is generalized to an “anisotropic distance”. This anisotropic distance yields an electrostatic potential with ellipsoidal equipotential surfaces and an electric field that is distorted from the radial direction by the tensor-valued, anisotropic permittivity. At the same time, the displacement current remains purely radially polarized. The exact solution of Coulomb’s law is generalized to a spherical-harmonics solution for compressional acoustic waves in elastic media and to a Yukawa-like solution for compressible fluids in Darcy-style flow in porous media. |

**Research activities and scientific results of the CCQCN**

Speaker: | Georgios Tsironis |

Department: | University of Crete |

Time: | Friday 13 December 2013 |

Venue: | The 3rd floor seminar room of the physics department |

Abstract: | This seminar will detail the quarterly reasearch activities and principle scientific results of the research conducted at the CCQCN to the research community of Heraklion. The intended audience will be members of the University of Crete, FORTH, the CCTP, and the CCQCN. |

**Research activities and scientific results of the CCTP**

Speaker: | Elias Kiritsis |

Department: | University of Crete |

Time: | Friday 13 December 2013 |

Venue: | The 3rd floor seminar room of the physics department |

Abstract: | This seminar will highlight the annual reasearch activities and principle scientific results of the research conducted at the CCTP to the research community of Heraklion. The intended audience will be members of the University of Crete, FORTH, the CCTP, and the CCQCN. The focus will be on the results of the ERC program "AdS/CMT". |